This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-195867 filed Jun. 29, 2000.
This invention relates to a vehicle electronic control unit and method, and particularly to a vehicle electronic control unit and method for measuring a soak time of an engine by using a timing part such as a clock IC (integrated circuit) which measures time continuously irrespective of whether a microcomputer is operating or stopped.
Electronic control units (ECUs) for vehicles use a built-in clock IC as a timing part or an external clock to measure elapsed time and use data from the clock IC to calculate a time period in which the ECU power supply has been turned off and a microcomputer held inoperative. This elapsed time is an engine stoppage time (soak time Ts).
In one proposal, the microcomputer reads in time measured by the clock IC at every predetermined interval (circle mark in FIG. 5) and stores this time data in a memory such as a standby RAM (SMAM) by updating. Thus, when an ignition (IG) switch is turned off, that is, the microcomputer is turned inoperative (time t11), the time data immediately before the turning off is held stored. When the IG switch is turned on again later (t12) to re-start the microcomputer operation, the microcomputer calculates the soak time Ts from the difference between the time data stored in the memory and the current time measured by the clock IC presently.
However, a power supply voltage of a battery falls temporarily when the engine is cranked by a starter. Thus, a main power supplied to the microcomputer falls below a predetermined voltage VMC required for the microcomputer to operate, and the microcomputer tends to be reset from time t13 to time t14. As a result, when the microcomputer starts operating after being reset, the soak time Ts which has already been calculated immediately after the turning on of the IG switch is calculated again. This recalculated soak time Ts becomes very short. This problem is phenomenal in winter when the battery power is lowered due to low ambient temperature.
It is therefore an object of the invention to provide an electronic control unit and method which can measure an engine soak time accurately.
According to the present invention, an electronic control unit for a vehicle has a timing part continuously supplied with an electric power to measure time, a control part operable to carry out a predetermined operation when the electric power is supplied, and a memory which stores the measured time. The memory continues to store the time data of the timing part measured immediately before an engine of the vehicle is stopped. The control part calculates a soak time of the engine from the stored time data and a current time data of the timing part when an engine cranking is completed. The completion of engine cranking may be detected from a rise of rotation speed of the engine to a predetermined speed.